The objectives during KH-10-6 were:
1) to verify the hypothesis that hydrogen-rich KHF is controlled by the ambient crustal structure and the chemical composition of lithosphere,
2) to estimate the chemical and microbiological fluxes from KHF to seawater through hydrothermal plumes,
3) to quest an unknown hydrothermal field on the rise, tentatively called Yokoniwa Rise, north of the KHF, and
4) to develop the survey method for hydrothermal activities using AUV.
We also surveyed the Edmond Hydrothermal Field about 140 km north of the KHF, where the fluids do not contain much hydrogen, for comparative study.
KH-10-6 cruise achieved brilliant success in attaining its scientific objectives. Most of the operations were completed successfully under the collaboration with the highly skilled Hakuho-maru crew.
Figure 1.3D bathymetry of the area
Preliminary results of the cruise
1) A r2D4 #68 dive was done successfully above the Yokoniwa Rise north of the Kairei Hydrothermal Field, where the dead chimneys on ultramafic exposure were discovered in 2009. High-resolution side scan image and interferometric bathymetry was obtained with data from chemical and physical sensors. The attached magnetometer could detect the positive anomaly on the dead chimney area.
2) Surface geophysical mapping revealed the detailed feature of CIR-4 segment, where no previous data existed. The result will improve our understanding of spreading history and structural segmentation of the CIR, and will provide a key to consider the tectonic setting of the Edmond Hydrothermal Field.
3) Total 80 mile of deep-tow magnetic profile was obtained across CIR-1 segment. The detailed spreading history since 2 Ma was revealed, that will constrain the evolution of detachment faults around the Kairei Hydrothermal Field.
4) A number of lower crust / mantle materials were collected around the Kairei Hydrothermal Field. Focused dredge hauls on the Yokoniwa Rise will lead us to a reliable model of Yokoniwa formation.
5) Systematic sampling of mid-ocean ridge basalts with fresh glass along the ridge axis will provide a good opportunity to study the mantle heterogeneity beneath the southern CIR.
6) Total ten CTD tow-yo surveys and three vertical casts could reveal the spread of hydrothermal plumes and their chemical and physical properties around the Kairei and Edmond Hydrothermal Fields. The anomalies of pH, turbidity, alkalinity, Mn,ΣCO2 and DO were detected around the Kairei Hydrothermal Field. Very high concentration of hydrogen was also confirmed.
7) Newly developed pH sensor and turbidity meter were attached to the wire during most of the dredge hauls and plankton net operations. Distinct turbidity anomalies were detected at some sites, that could prove the effectiveness of “dredge-attached” sensors.
8) Approximately double-dense microbial cell density was detected within the hydrothermal plume above the Kairei Hydrothermal Field. The detailed distribution will provide a new insight into microbiological flux through the plume.
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